technical service training global...

Student Information

FCS-13195-REF CG7965/S en 12/2001

Technical Service Training

Global FundamentalsCurriculum Training – TF1010009S

Engine Operation

Introduction Preface

Service Training 1

Global fundamentals training overview

The goal of the Global Fundamentals Training is to provide students with a common knowledge base of the

theory and operation of automotive systems and components. The Global Fundamentals Training Curriculum

(FCS-13203-REF) consists of nine self-study books. A brief listing of the topics covered in each of the self-study

books appears below.

� Shop Practices (FCS-13202-REF) explains how to prepare for work and describes procedures for lifting

materials and vehicles, handling substances safely, and performing potentially hazardous activities (such as

welding). Understanding hazard labels, using protective equipment, the importance of environmental policy,

and using technical resources are also covered.

� Brake Systems (FCS-13201-REF) describes the function and operation of drum brakes, disc brakes, master

cylinder and brake lines, power-assist brakes, and anti-lock braking systems.

� Steering and Suspension Systems (FCS-13196-REF) describes the function and operation of the power-

assisted steering system, tires and wheels, the suspension system, and steering alignment.

� Climate Control (FCS-13198-REF) explains the theories behind climate control systems, such as heat transfer

and the relationship of temperature to pressure. The self-study also describes the function and operation of the

refrigeration systems, the air distribution system, the ventilation system, and the electrical control system.

� Electrical Systems (FCS-13197-REF) explains the theories related to electricity, including the characteristics

of electricity and basic circuits. The self-study also describes the function and operation of common

automotive electrical and electronic devices.

� Manual Transmission and Drivetrain (FCS-13199-REF) explains the theory and operation of gears.

The self-study also describes the function and operation of the drivetrain, the clutch, manual transmissions

and transaxles, the driveshaft, the rear axle and differential, the transfer case, and the 4x4 system.

� Automatic Transmissions (FCS-13200-REF) explains the function and operation of the transmission and

transaxle, the mechanical system, the hydraulic control system, the electronic control system, and the transaxle

final drive. The self-study also describes the theory behind automatic transmissions including mechanical

powerflow and electro-hydraulic operation.

� Engine Operation (FCS-13195-REF) explains the four-stroke process and the function and operation of the

engine block assembly and the valve train. Also described are the lubrication system, the intake air system,

the exhaust system, and the cooling system. Diesel engine function and operation are covered also.

� Engine Performance (FCS-13194-REF) explains the combustion process and the resulting emissions.

The self-study book also describes the function and operation of the powertrain control system, the fuel

injection system, the ignition system, emissions control devices, the forced induction systems, and diesel

engine fuel injection. Read Engine Operation before completing Engine Performance.

To order curriculum or individual self-study books, contact Helm Inc.

Toll Free: 1-800-782-4356 (8:00 am – 6:00 pm EST)

Mail: 14310 Hamilton Ave., Highland Park, MI 48203 USA

Internet: www.helminc.com (24 hours a day, 7 days a week)

Contents Introduction

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Introduction.................................................................................................................................. 1Preface ...................................................................................................................................................................... 1

Global fundamentals training overview .......................................................................................................... 1Contents .................................................................................................................................................................... 2

Lesson 1 – Internal combustion engine ...................................................................................... 5General ............................................................................................................................................................ 5Objectives ........................................................................................................................................................ 5

At a glance ................................................................................................................................................................ 6Purpose and function ....................................................................................................................................... 6

Theory ....................................................................................................................................................................... 7Gasoline internal combustion engine .............................................................................................................. 7

Operation.................................................................................................................................................................. 8Creating mechanical motion ........................................................................................................................... 8The four-stroke cycle ...................................................................................................................................... 9Bore, stroke and displacement ...................................................................................................................... 10Stroke ............................................................................................................................................................ 10Displacement ................................................................................................................................................. 11Intake stroke .................................................................................................................................................. 12Compression stroke ....................................................................................................................................... 12Compression ratio ......................................................................................................................................... 13Power stroke .................................................................................................................................................. 14Exhaust stroke ............................................................................................................................................... 14

Summary ................................................................................................................................................................ 15

Lesson 2 – Engine block assembly ............................................................................................ 16General ................................................................................................................................................................... 16

Objectives ...................................................................................................................................................... 16At a glance .............................................................................................................................................................. 17

Engine block assembly .................................................................................................................................. 17Components............................................................................................................................................................ 18

Major components ......................................................................................................................................... 18Engine block liners ........................................................................................................................................ 19Crankcase ...................................................................................................................................................... 21Crankshaft ..................................................................................................................................................... 21Main bearing journals ................................................................................................................................... 22Vibration damper ........................................................................................................................................... 23Connecting rods ............................................................................................................................................ 26Cylinder wall lubrication .............................................................................................................................. 28Pistons ........................................................................................................................................................... 29Piston rings .................................................................................................................................................... 31

Lesson 3 – Valve train ................................................................................................................ 34General ................................................................................................................................................................... 34


Valve train types overview ............................................................................................................................ 35Overhead camshaft (OHC) configuration ..................................................................................................... 38Single overhead cam (SOHC) ....................................................................................................................... 39Double overhead cam (DOHC) ..................................................................................................................... 39Camshaft drives ............................................................................................................................................. 39

Components............................................................................................................................................................ 40Pushrod type (OHV) cylinder head ............................................................................................................... 40Cylinder head gasket ..................................................................................................................................... 41Head bolts ...................................................................................................................................................... 41Valves ............................................................................................................................................................ 42Valve seats ..................................................................................................................................................... 43Valve stem ..................................................................................................................................................... 44Valve guide .................................................................................................................................................... 45Valve clearance .............................................................................................................................................. 46

Introduction Contents

Service Training 3

Valve springs ................................................................................................................................................. 47Spring tension................................................................................................................................................ 48Working height .............................................................................................................................................. 48Camshaft ....................................................................................................................................................... 49Lift ................................................................................................................................................................. 49Duration ......................................................................................................................................................... 50Overlap .......................................................................................................................................................... 51Overhead valve drive ..................................................................................................................................... 52Pushrods ........................................................................................................................................................ 53Rocker arms .................................................................................................................................................. 53Valve lifters ................................................................................................................................................... 54Solid lifter ..................................................................................................................................................... 54Hydraulic lifters and buckets ........................................................................................................................ 55Roller versus flat lifters ................................................................................................................................. 56Overhead camshaft (OHC) cam followers .................................................................................................... 57Bucket-type solid lifters ................................................................................................................................ 57Overhead camshaft (OHC) hydraulic lash adjusters ..................................................................................... 58Rocker arm-mounted hydraulic lash adjuster ............................................................................................... 59Overhead cam drive ...................................................................................................................................... 60Belt and chain drive....................................................................................................................................... 61Belt and gear drive ........................................................................................................................................ 62

Theory ..................................................................................................................................................................... 63Variable cam timing ...................................................................................................................................... 63

Lesson 4 – Lubrication system.................................................................................................. 64General ................................................................................................................................................................... 64


Description .................................................................................................................................................... 65Theory ..................................................................................................................................................................... 66

Motor oil ........................................................................................................................................................ 66Operation................................................................................................................................................................ 68

Oil circulation ............................................................................................................................................... 70Pressure lubrication ....................................................................................................................................... 71Stresses on the oil .......................................................................................................................................... 72Oil changes .................................................................................................................................................... 73

Components............................................................................................................................................................ 73Oil pan components ....................................................................................................................................... 73Oil strainer ..................................................................................................................................................... 73Oil pump........................................................................................................................................................ 74Oil pump types .............................................................................................................................................. 75Oil filter ......................................................................................................................................................... 77Oil seals ......................................................................................................................................................... 80Dipstick ......................................................................................................................................................... 80Oil pressure warning indicator ...................................................................................................................... 80

Lesson 5 – Intake air system ..................................................................................................... 81General ................................................................................................................................................................... 81


Air intake system........................................................................................................................................... 82Components............................................................................................................................................................ 84

Inlet runners .................................................................................................................................................. 84Variable Induction Systems ........................................................................................................................... 84Intake manifold runner control (IMRC) system ........................................................................................... 85Intake manifold tuning (IMT) valve ............................................................................................................. 86Forced induction ............................................................................................................................................ 87

Theory ..................................................................................................................................................................... 88Turbocharging ............................................................................................................................................... 88

Contents Introduction

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Lesson 6 – Exhaust system ........................................................................................................ 91General ................................................................................................................................................................... 91


Description and Purpose ............................................................................................................................... 92Components............................................................................................................................................................ 94

Mufflers ......................................................................................................................................................... 94Catalytic converter ........................................................................................................................................ 94

Lesson 7 – Cooling system......................................................................................................... 95General ................................................................................................................................................................... 95


Description .................................................................................................................................................... 96Operation ....................................................................................................................................................... 98

Components............................................................................................................................................................ 99Coolant pump ................................................................................................................................................ 99Thermostat ................................................................................................................................................... 100Cooling fan .................................................................................................................................................. 102Cooling fan drives ....................................................................................................................................... 102Coolant overflow reservoir and degas bottle ............................................................................................... 104Degas bottle ................................................................................................................................................. 105Radiator ....................................................................................................................................................... 108

Lesson 8 – Diesel engine .......................................................................................................... 111General ................................................................................................................................................................. 111

Objectives .................................................................................................................................................... 111At a glance ............................................................................................................................................................ 112

Description .................................................................................................................................................. 112Operation ..................................................................................................................................................... 112

Components.......................................................................................................................................................... 113Cylinder block ............................................................................................................................................. 113Wet liners .................................................................................................................................................... 114Crankshaft ................................................................................................................................................... 114Connecting rods .......................................................................................................................................... 115Pistons and rings ......................................................................................................................................... 115Cylinder head .............................................................................................................................................. 115Open combustion chamber design .............................................................................................................. 116Pre-combustion chamber design ................................................................................................................. 117Valves and seats ........................................................................................................................................... 118

At a glance ............................................................................................................................................................ 119Fuel delivery system ................................................................................................................................... 119Lubrication system ...................................................................................................................................... 121Cooling system ............................................................................................................................................ 122Fuel injection ............................................................................................................................................... 124

Lesson 9 – Diagnostic process ................................................................................................. 125General ................................................................................................................................................................. 125

Objectives .................................................................................................................................................... 125Overview ............................................................................................................................................................... 126

Symptom-to-system-to-component-to-cause diagnostic process ............................................................... 126Workshop literature ..................................................................................................................................... 127

List of abbreviations ................................................................................................................ 128

Service Training 5

Lesson 1 – Internal combustion engine General

Objectives

Upon completion of this lesson, you will be able to:

� Explain the purpose and function of the internal combustion engine.

� Describe the types of internal combustion engines.

� Explain the process by which burning fuel is turned into rotary motion.

� Explain the purpose of an engine.

� Identify the major components and systems of an internal combustion engine.

� Explain the process by which rotary motion is transferred from the engine to the vehicle wheels.

� Describe the four-stroke cycle.

6 Service Training

At a glance Lesson 1 – Internal combustion engine

Purpose and function

The internal combustion engine provides power to

move the vehicle. A typical internal combustion

engine is either a gasoline or diesel design. The type

of fuel used in gasoline and diesel engines is different

because of the method used for ignition of the fuel.

The mechanical operation of each engine is nearly

identical. In an engine, fuel is burned to create

mechanical motion. The major components of the

internal combustion engine include:

� Cylinder block assembly

� Valve train

� Intake system

� Exhaust system

� Lubrication system

� Cooling system

Service Training 7

Lesson 1 – Internal combustion engine Theory

Gasoline internal combustion engine

The combustion process

Combustion is the process of igniting a mixture of air

and fuel. In the combustion process a mixture of air

and fuel is drawn into a cylinder and compressed by a

moving piston. The compressed mixture is ignited to

create energy for vehicle motion.

Intake stroke

1 Spark plug

2 Exhaust valve (closed)

3 Intake valve (open)

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Operation Lesson 1 – Internal combustion engine

Creating mechanical motion

When combustion occurs, the gases from the burning

air-fuel mixture expand in the cylinder with very high

pressure. The high pressure pushes the piston down in

the cylinder. The piston is connected to a connecting

rod, which is connected to the crankshaft. Because the

piston is connected in this way to the crankshaft, the

crankshaft begins to rotate with the motion of the

piston. The connecting rod and crankshaft convert the

up and down motion of the piston into rotary motion.

As combustion occurs in each cylinder, pulses of

energy are transferred from the pistons to the

crankshaft. The flywheel, which is a heavy round

metal plate attached to one end of the crankshaft,

helps smooth out the power pulses and keeps the

crankshaft rotating smoothly. The rotary motion from

the engine is transferred to the wheels through the

transmission and drivetrain.

Mechanical motion

1 Engine block

2 Flywheel

3 Crankshaft

4 Connecting rod

5 Piston

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Lesson 1 – Internal combustion engine Operation

The four-stroke cycle

The four-stroke cycle

1 Intake stroke

2 Compression stroke

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3 Power stroke

4 Exhaust stroke

Nearly all modern vehicle engines are four-stroke

cycle engines. Four-stroke means the piston moves

the length of the cylinder four times in order to

complete one combustion cycle.

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Bore, stroke and displacement

Cylinder bore

In automotive engine terminology, bore refers to

cylinder bore. Cylinder bore is the diameter of the

cylinder.

Cylinder bore measurement

1 Cylinder bore

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Stroke

Piston stroke

Stroke refers to piston stroke. Piston stroke is a

measurement of the distance a piston travels in the

cylinder during crankshaft rotation. The stroke is

equal to the distance the piston travels in the cylinder

from the lowest point to the highest point.

The highest point of the piston in the cylinder is

called top dead center (TDC). The lowest point of the

piston in the cylinder is called bottom dead center

(BDC). One stroke of a piston takes one half-turn of

the crankshaft, or 180 degrees rotation.

Service Training 11


Displacement

Displacement

1 Cylinder and combustion chamber volume at BDC

2 Cylinder and combustion chamber volume at TDC

The term displacement refers to two related concepts.

Cylinder displacement is the amount of air that is

moved or displaced by the piston in a single cylinder

when it moves from BDC to TDC in the cylinder.

Displacement is expressed as a volume in liters (L),

cubic centimeters (cc), or cubic inches (ci).

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3 Top of piston at TDC

4 Top of piston at BDC

Total engine displacement is equal to the

displacement of one piston multiplied by the total

number of cylinders in the engine. For example, each

cylinder of a certain four-cylinder engine has a

displacement of 0.500 liter. Therefore, total engine

displacement is equal to cylinder displacement

(0.500 liter) times the number of cylinders (4), or

2.0 liters.

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Intake stroke

The intake stroke is considered the first of the four

cycles. The rotating crankshaft pulls the piston down

from TDC toward BDC. The exhaust valve is closed

and the intake valve is open. As the piston moves

down, the air-fuel mixture is drawn into the cylinder

through the intake valve.

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Piston and valves during intake stroke

1 Intake valve open

2 Exhaust valve closed

3 Piston moves downward

Compression stroke

When the piston reaches BDC, the intake stroke ends

and the compression stroke begins. The intake valve

closes and the exhaust valve stays closed. The

crankshaft motion sends the piston back up the

cylinder toward TDC. The air-fuel mixture is trapped

in the cylinder and is compressed between the piston

and cylinder head.

Compression of the air-fuel mixture is very important

for developing power. The greater the compression,

the more power the mixture creates during

combustion. Compression also “pre-heats” the

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Piston and valves during compression stroke

1 Intake valve closed


3 Piston moves upward

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Compression ratio

Compression ratio

1 Volume before compression

2 Volume after compression

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3 Piston at TDC

4 Piston at BDC

The compression ratio indicates how much the air-

fuel mixture is squeezed during the compression

stroke. The compression ratio is the volume at TDC

compared to the volume at BDC during the

compression stroke. For example, a compression ratio

of 8 to 1 means the volume at BDC is eight times

larger than the volume when the piston is at TDC.

Higher compression ratios allow for greater potential

power output.

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Power stroke

Just before the piston reaches TDC, a spark from the

spark plug ignites the air-fuel mixture and the power

stroke begins. The burning gases expand rapidly,

creating very high pressure on top of the piston as the

piston rotates past TDC and moves down the cylinder

toward BDC. The intake and exhaust valves remain

tightly closed, so all the force is pushing the piston

down in the cylinder to turn the crankshaft.

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Piston and valves during power stroke



3 Combustion

4 Piston moves downward

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Piston and valves during exhaust stroke


2 Exhaust valve open

3 Piston moves upward

Exhaust stroke

As the piston nears BDC on the power stroke, the

exhaust valve begins to open. As the piston passes

BDC, the rotating crankshaft pushes the piston back

up the cylinder toward TDC and the exhaust valve is

fully opened. The piston pushes the burned gases out

the exhaust valve, through the cylinder head exhaust

port and out the exhaust system.

As the piston passes TDC, the four-stroke cycle

begins again with the intake stroke. The exhaust valve

stays open momentarily at the beginning of the intake

stroke, allowing the momentum of the gases to empty

the cylinder completely.

Service Training 15

Lesson 1 – Internal combustion engine Summary

Summary

We have illustrated the four-stroke cycle in only one

cylinder. Remember, the four strokes are continuously

repeated in all the cylinders in an alternating pattern.

The four strokes of the cycle — intake, compression,

power, and exhaust —require two full rotations of the

crankshaft. However, the piston receives direct

combustion pressure only during the power stroke, or

about one quarter of the cycle.

When you realize that no power is being generated

during three of the four strokes, you can see why the

flywheel is so important. The flywheel “stores” the

energy that is generated. The flywheel uses the stored

energy to keep the crankshaft rotating smoothly.

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General Lesson 2 – Engine block assembly

Objectives


� Explain the purpose and function of the engine block assembly.

� Describe the different types of engine block assemblies.

� Identify the major components of the engine block assembly.

� Explain the theory and operation of the engine block assembly.

Service Training 17

Lesson 2 – Engine block assembly At a glance

Engine block assembly

The engine block is the main supporting member of

the engine. Almost every other engine component is

either connected to or supported by the engine block.

The pistons, connecting rods, and crankshaft work

inside the engine block.

The engine block may be either an in-line or “V” type

design depending upon the arrangement of the

individual cylinders in the block.

The engine block contains the cylinders, internal

passages for coolant and oil, and mounting surfaces

for attaching engine accessories, such as the oil filter

and coolant pump. The cylinder head is mounted on

top of the engine block, and the oil pan is mounted on

the bottom.

Engine block assembly

1 Engine block

2 Flywheel

3 Crankshaft

4 Connecting rod

5 Piston

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Components Lesson 2 – Engine block assembly

Major components

In-line engine block design

In-line engines commonly have 3, 4, 5 or

6 cylinders.

V-Type engine block design

A V-Type engine design has two banks of cylinders

arranged in a “V” pattern. Even though the cylinders

are in two banks, they are still connected to a

common crankshaft.

V-configuration engines commonly have 6, 8, and

occasionally 12 cylinders.

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Four-cylinder in-line engine block

1 Cylinders

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V-6 engine block

1 Cylinders

Service Training 19

Lesson 2 – Engine block assembly Components

Engine block and liner

Cylinder liners

Some engine designs use cylinder liners. A cylinder

liner is a hardened steel cylinder which is inserted

into the engine block. A liner is not required in all

engine blocks. Liners are made of a hard material to

contain combustion inside the cylinders and reduce

wear from piston ring movement. There are two types

of cylinder liners: wet liners, and dry liners.

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Engine block and liner

1 Cylinder liner

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Wet liner

1 Liner

2 Seal

3 Coolant

4 Engine block

Wet liners

Wet liners are so named because they come into direct

contact with engine coolant in the block. Seals are

used to prevent coolant from reaching the crankcase.

Wet liners are easy to repair since they can be fairly

easily changed. This makes it unnecessary to machine

the cylinder and eliminates the need for oversized

pistons. Wet liners have an increased chance for

corrosion because of their design.

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Engine block and liner (continued)

Dry liners

Dry liners do not come into direct contact with engine

coolant. Dry liners are installed in an engine block by

either pressing or shrinking.

The process of shrink-fitting uses the property of

metals that allows them to shrink when cold and

expand when hot. The dry liner is cooled and the

engine block is heated, then the liner is inserted into

the block. This method makes it easier to replace the

liners.

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Dry liner

1 Liner

2 Coolant

3 Engine block

Service Training 21


Crankcase

The crankcase supports the crankshaft and main

bearings. The bottom of the engine block forms the

upper part of the crankcase. The oil pan attached to

the bottom of the engine block forms the bottom part

of the crankcase. The crankcase includes several

support surfaces for the crankshaft. The number of

supports varies depending on the length of the

crankshaft and cylinder layout. For example, a four-

cylinder engine usually has five of these support

surfaces. The crankshaft mounts on insert bearings

that are installed on the support surfaces and attached

with bearing caps. The supports have oil passages that

lubricate the crankshaft as it spins against the

bearings. These passages align with oil holes in the

bearings. The engine block includes a groove for the

rear main oil seal, which keeps oil from leaking out at

the rear of the crankshaft. The term “main” refers to

bearings, seals, and other mounting hardware used on

the crankshaft. “Main” distinguishes these mounting

parts from other mounting parts that connect to the

crankshaft, such as connecting rod bearings.

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Crankcase components

1 Engine block

2 Thrust bearings

3 Crankshaft

4 Main bearing caps

5 Main bearing cap mounting bolt

6 Main bearings

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Crankshaft

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Crankshaft (typical)

1 Front end

2 Oil passage

3 Connecting rod journal

4 Flywheel end

5 Main bearing journal

The crankshaft changes the up-and-down motion of

the pistons into the rotational motion needed to drive

the wheels of the vehicle. The crankshaft is mounted

in the engine block on “U” shaped supports that are

cast into the engine block assembly. Caps called main

bearing caps are bolted onto the supports to secure the

crankshaft onto the block. Between the crankshaft and

its mounting surfaces are bearings in which the

crankshaft is held and is able to spin. When the block

is manufactured, main bearing surfaces are machined

to be exactly parallel to the crankshaft. For this

reason, main bearing caps must never be

interchanged.

The crankshaft withstands the tremendous forces of

the pistons’ power strokes. The crankshaft is usually

made of heavy, high-strength cast iron. Crankshafts

made for high performance or heavy-duty

applications usually are made of forged steel. Some

crankshafts have counterweights cast opposite the

crankpins. Counterweights help balance the

crankshaft and prevent vibration during high-speed

rotation.

Service Training 23


Main bearing journals

Main bearing journals on a crankshaft are highly

polished and manufactured to exact roundness so they

rotate properly in the bearing inserts. Oil passages

drilled into the main journals receive oil flow from

the supports in the engine block. Slanted oil passages

are drilled from the main journals to the crankpin

journals to lubricate the connecting rod bearings.

Thrust bearings

In addition, one of the main journals (usually in the

middle or rear) is machined with a thrust surface. This

surface rides against a special thrust bearing to limit

front-to-rear movement of the crankshaft.

Crankshaft journals

The journals on a crankshaft are those areas which

serve as bearing surfaces for the crankshaft itself, or

the connecting rods which are attached to the

crankshaft. The journals for crankshaft bearings are

referred to as main bearing journals. The journals for

connecting rods are referred to as connecting rod

journals.

A common design for an in-line 4-cylinder engine has

five main bearing journals and four connecting rod

journals. One piston is connected to each connecting

rod journal using a connecting rod. V-type cylinder

design engines attach two connecting rods to each

connecting rod journal.

Crankshaft journals

1 Connecting rod journal

2 Crank web

3 Crankshaft counterweights

4 Main bearing journal

5 Balance weight

6 Balance hole

7 Oil bore

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Main bearing journals (continued)

Main bearings

Main bearings support the crankshaft into the main

bearing journals and main bearing caps. Crankshaft

main bearings are split circular sleeves that wrap

around the crankshaft main journals. The upper half

of the bearing has one or more oil holes which allow

lubricant to coat the inside surface of the bearing. The

upper bearing fits into a main support on the bottom

of the engine block. The lower half of the bearing fits

into the bearing cap. The wear surfaces of the

bearings are made of softer material than the

crankshaft. The softer material reduces friction, and it

tends to mold itself around any uneven areas on the

main journal. In addition, if wear does occur, it affects

the bearing, which is cheaper to replace than the

crankshaft.

Bearing lubrication

In most engines, the upper and lower bearings are not

interchangeable. The upper bearing usually has an oil

passage hole in it, allowing oil to flow to the bearing

surface of the main journal. Since the crankshaft main

journal diameter is a few hundredths of a millimeter

smaller than the inside diameter created by the

bearings, oil can coat the entire bearing surface.

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Crankshaft main bearings

1 Upper main bearing

2 Oil hole

3 Lower main bearing

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Crankshaft main bearings installed

1 Oil passage upper main bearing

2 Upper main bearing

3 Oil film

4 Lower main bearing

5 Crankshaft main journal

6 Bearing clearance

Service Training 25


Bearing clearance

The gap between the bearings and crankshaft journal

is called bearing clearance. Clearance is one of the

most critical measurements in the engine. The oil that

lubricates the bearings does not actually stay in a

continuous film. As the crankshaft turns, the oil works

its way to the outer edges of the bearings, where it is

thrown off into the crankcase. New oil constantly

feeds through the oil hole to replace the oil thrown

off. The constant flow of oil over the bearings helps

cool them and flush away grit and dirt from the

bearing surfaces. If the clearance is too small, not

enough oil is allowed in to lubricate the bearings. The

resulting friction wears out the bearings quickly. If

the clearance is too large, too much oil flows through

the bearings. Oil pressure drops and the crankshaft

journal may start to pound against the bearing rather

than spin inside it. To prevent damage to the bearings

and crankshaft, bearing clearances are set precisely

whenever the bearings or crankshaft are repaired.

Thrust bearings

In addition to rotating, the crankshaft tends to move

back and forth. Since this type of motion has a

negative effect on the crankshaft associated

components measures are taken to limit back and

forth motion. One of the main journals on the

crankshaft is machined to accept a thrust bearing. The

thrust bearing keeps the crankshaft from moving back

and forth. The upper and lower thrust bearings have

oil grooves that allow oil to flow around the journal.

Crankshaft main bearings

1 Upper thrust bearing

2 Crankshaft

3 Lower thrust bearing

4 Crankshaft main bearings (lower)

5 Crankshaft main bearings (upper)

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Vibration damper

Crankshaft vibration damper

1 Rubber

2 Timing belt pulley

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3 Crankshaft

4 Vibration damper

Even though the crankshaft is very strong, it has a

certain amount of flexibility. During a power stroke

the crankshaft actually twists slightly then springs

back. At a normal hot idle, this twisting and

untwisting may repeat five times every second. When

accelerating under load, the cycle may occur 25 or 30

times per second. The twisting and untwisting causes

vibrations. The vibration damper, which is usually

mounted on the front end of the crankshaft, works to

minimize these crankshaft vibrations.

Service Training 27


Connecting rods

The connecting rod transfers the movement of the

piston to the crankpin on the crankshaft. A steel

piston pin connects the piston to the connecting rod.

The piston pin allows the piston to pivot on the small

end of the connecting rod. The large end of the

connecting rod is connected to the crankshaft with a

connecting rod bearing cap. The cap is very similar in

design and function to the main bearing caps. The

connecting rod bearings are similar to the crankshaft

main bearings.

Connecting rod

1 Connecting rod

2 Crankshaft

3 Oil pan

4 Cylinder block

5 Piston pin

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28 Service Training


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Cylinder wall lubrication

An oil jet in the connecting rod lubricates the cylinder

walls and cools the piston. Some engine designs use

oil splash to lubricate and cool the cylinder walls.

Crankshaft oil passages deliver oil to the connecting

rod journals. When the bearing holes match up with

the oil hole in the connecting rod journal, pressurized

oil squirts through the oil jet.

Connecting rod oiling

1 Oil holes

2 Connecting rod

3 Oil jet

4 Upper connecting rod bearing

5 Lower connecting rod bearing

Service Training 29


Pistons

The piston top forms the bottom of the combustion

chamber in the cylinder. The piston transfers the

power created by the burning air-fuel mixture to the

crankshaft.

The top surface of the piston is called the head, or

crown. The upper part of the piston contains several

grooves where the compression rings and oil ring fit.

The lower part of the piston, under the rings, is called

the skirt. Thrust surfaces on the skirt guide the piston

in the cylinder bore and prevent the piston from

rocking back and forth in the cylinder. Most pistons

have a mark on one side or the top that identifies the

side of the piston that faces the front of the engine.

The piston pin is inserted through the piston pin bore

to connect the piston to the connecting rod. In some

piston designs, the pin bore is offset slightly from the

center of the piston. The offset helps stabilize the

piston as it moves up and down in the cylinder.

Piston clearance

Although the piston fits closely in the cylinder bore, it

does not completely seal the combustion chamber.

The seal is accomplished using the piston rings

installed in grooves near the top of the piston. To

allow room for the piston rings and lubricating oil, a

clearance must be maintained between the outside

edge of the piston and the cylinder wall. This

clearance lets lubricating oil into the upper part of the

cylinder. The clearance also prevents the engine from

seizing if one of the pistons expands too much from

overheating. Two types of piston design are used to

control heat expansion: tapering, and cam grinding.

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Piston features

1 Head

2 Piston pin bore

3 Piston ring grooves

4 Thrust surface

5 “Front” mark

6 Center of piston

7 Center of piston pin bore

8 Offset

9 Skirt

30 Service Training


Pistons (continued)

Tapered pistons

To maintain a consistent clearance from the top to the

bottom of the cylinder, the piston usually has a slight

tapered shape. The top diameter of the piston is

slightly smaller than the bottom diameter when the

piston is cold. When the engine operates, the top of

the piston gets much hotter than the bottom, and the

expansion at the top evens up the diameter.

Tapered piston

1 Top diameter (smaller)

2 Bottom diameter (larger)

Cam-ground piston

1 Piston pin bore

2 Large diameter

3 Small diameter

Cam-ground pistons

Another technique used to make the piston fit better

in the cylinder and control heat expansion is called

cam grinding. Cam-ground pistons are manufactured

so that they have a slightly oval shape. The piston is

designed to expand in the direction of the small

diameter when heated, making the piston more round

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Service Training 31


Piston rings

Piston rings

1 Top compression ring

2 Second compression ring

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3 Scuff rings on oil ring

4 Expander on oil ring

Piston rings seal the combustion chamber where the

air-fuel mixture is ignited. In addition to sealing the

combustion chamber, piston rings scrape oil from the

cylinder walls and direct it back into the crankcase.

Piston rings also help transfer heat from the piston to

the cylinder walls.

The top two rings are called compression rings. They

are usually made of cast iron with chrome plating on

the surface facing the cylinder wall. Compression

rings are available with different edge shapes. The

bottom ring is called an oil ring. The oil ring is

usually made up of several parts assembled in a

specific order in the same piston groove. A typical oil

ring is made up of two scuff rings separated by an

expander.

32 Service Training


Piston rings (continued)

Compression rings

Compression ring oil control

1 Intake or power stroke

2 Compression rings scrape cylinder wall

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4 Compression rings skim over oil film

Compression rings seal the combustion chamber,

scrape the cylinder walls clean, and transfer heat from

the piston to the cylinder wall. When the piston is

moving down the cylinder during the intake stroke the

lower edges of the compression rings scrape off any

oil that was not recovered by the oil ring. On the

compression and exhaust strokes, the compression

rings skim over the oil film so the oil is not pushed

into the combustion chamber. During the power

stroke, the rings create a tight seal for the combustion

chamber. The rings also create a path for heat to flow

from the piston to the cylinder wall.

Service Training 33


Oil rings

Oil ring assembly

1 Oil rings

2 Expander ring

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Oil rings control the lubrication of the cylinder walls

and direct oil back to the crankcase. Oil is constantly

sprayed or splashed onto the walls of the cylinders to

provide lubrication between the piston rings and

cylinder wall. The amount of oil on the cylinder wall

cannot fit into the space between the piston and

cylinder when the piston moves toward BDC and

therefore needs some place to go. The oil ring

provides a path for the oil to return to the crankcase.

As oil is scraped from the cylinder wall by the

compression rings, it flows behind the top expander

ring and into holes in the oil ring groove. These holes

direct oil to the open space inside the piston skirt. The

oil then drains back into the crankcase.

To properly seal the cylinder for compression and to

control oil bypass, the ring end-gaps are staggered.

34 Service Training

General Lesson 3 – Valve train

Objectives


� Explain the purpose and function of the valve train.

� Describe valve train types.

� Describe the Overhead Valve (OHV) train configuration.

� Describe the Overhead Camshaft (OHC) configuration.

Service Training 35

Lesson 3 – Valve train At a glance

Valve train types overview

OHC and pushrod-type camshaft drives

1 OHC: the camshaft(s) are located in the

cylinder head(s).

2 OHV: the single camshaft is located in the

cylinder block.

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Air and fuel enter and exit the combustion chamber

through valve ports. Valves, located at the combustion

chamber side of the port, open and close to either

allow flow or tightly seal the combustion chamber.

The valves must open and close at the correct times

for proper engine function. Valve timing is

accomplished by the camshaft acting on the valve

train.

There are two main types of valve trains used in

automotive engines. The two types are Overhead

Valve (OHV), and Overhead Camshaft (OHC). The

OHV type valve train uses a single camshaft centrally

located in the cylinder block. The camshaft lobes

control the opening and closing events of the valves in

the cylinder head through a series of linking

mechanical components. The OHC type valve train

uses one or more camshafts attached directly to the

cylinder head above the valves. Valve opening and

closing events are controlled by camshaft lobes.

36 Service Training

At a glance Lesson 3 – Valve train

Valve train types overview (continued)

Pushrod-type valve (OHV) configuration

Pushrod-type engines, also known as Overhead Valve

(OHV) engines, have a single camshaft located in the

cylinder block. The valves are located in the cylinder

head above the combustion chamber. Valves are

opened and closed by camshaft lobes acting on lifters,

pushrods, and rocker arms.

The major components of the OHV valvetrain

include:

� Cylinder head

� Valves

� Valve seats

� Valve guides

� Valve springs

� Camshaft

� Pushrods

� Lifters

� Rocker arms

� Camshaft drives

� Overhead valve drive

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Pushrod-type valve train

1 Rocker arm

2 Valve

3 Camshaft

4 Cam lobe

5 Lifter

6 Pushrod

Service Training 37


Engines have passages that let the air-fuel mixture

into the cylinders and let exhaust gases out after the

mixture has burned. These passages, called valve

ports, seal very tightly during parts of the four-stroke

cycle. The valves must open and close the ports at

precise times.

As the camshaft turns, the cam lobe moves against the

lifter. The lifter pushes up on the pushrod, which

pushes up on one end of the rocker arm. The other

end of the rocker arm pushes down on the valve stem

and causes the valve to overcome spring pressure and

move to the open position. As the cam lobe moves

past the lifter, the valve spring pushes against the

valve, pushrod, rocker arm, and lifter. When the cam

lobe has rotated far enough, the valve closes tight

against the valve seat.

38 Service Training

At a glance Lesson 3 – Valve train

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Overhead camshaft (OHC) configuration

Camshaft drives

1 Chain driven SOHC

2 Chain driven DOHC

3 Belt driven DOHC

OHC engines have the camshaft(s) located in the

cylinder head.

The benefits of an overhead camshaft include:

� Fewer components in the valve train

� More precise and direct valve actuation

� Reduce frictional losses

Service Training 39


Single overhead cam (SOHC)

SOHC engines normally actuate two valves per

cylinder. SOHC engines use roller finger followers

which sit below the camshaft, or use rocker arms

which sit above the camshaft.

Double overhead cam (DOHC)

DOHC engine design divides the job of valve opening

between two camshafts. DOHC engines normally

actuate four valves per cylinder. More valves per

cylinder allows more efficient intake of the air and

fuel mixture during the intake stroke, and removal of

exhaust gases during the exhaust stroke.

DOHC engines use either roller finger followers or

direct acting mechanical buckets to actuate the valves.

Camshaft drives

The task of the engine timing system is to coordinate

the induction of the air and fuel mixture and the

expulsion of the exhaust gases with the up and down

motion of the piston. This is accomplished by

synchronizing the rotation of the crankshaft with the

camshaft(s). Since the crankshaft makes two

revolutions for each combustion cycle, and the

camshaft makes one revolution, the gear ratio must

always be 2:1. Valve opening and closing times are

indicated in crankshaft degrees. There are various

ways of driving the camshaft. The valve gear can be

driven by:

� Timing gears

� Timing chain

� Timing belt

Double overhead camshafts

1 Camshaft

2 Lifter

3 Cam lobe

4 Valve

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40 Service Training

Components Lesson 3 – Valve train

Pushrod type (OHV) Cylinder head

The cylinder head is bolted on top of the cylinder

block to form the roof of the combustion chamber.

The cylinder head:

� seals the tops of the cylinders.

� holds the spark plugs.

� provides seats, guides, and ports for the intake and

exhaust valves.

� holds the valve train.

� provides mountings for the intake and exhaust

manifolds.

Like the cylinder block, the cylinder head is made of

cast iron or aluminum alloy. The intake and exhaust

manifolds are mounted to the cylinder head, against

the valve ports. Most V-6 or V-8 engines have two

cylinder heads, one for each bank of cylinders. The

top part of the cylinder head is manufactured so that

the valve rocker arms or other parts of the valve train

can be mounted on it. OHV multi-valve cylinder head

1 Valve spring collets

2 Valve spring retainer

3 Valve spring

4 Valve seal

5 Rocker arm

6 Pushrod

7 Valve

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Service Training 41

Lesson 3 – Valve train Components

Cylinder head gasket

The cylinder head gasket forms the gas and watertight

junction between the cylinder head and the cylinder

block. In addition, the cylinder head gasket offsets

any minor irregularities in the mating surfaces. For

this reason the cylinder head gasket must be made of

a somewhat flexible material.

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Cylinder head gasket

1 Cylinder block

2 Cylinder head gasket

Head bolts

Cylinder head bolts hold the cylinder head firmly to

the cylinder block. There are two types of cylinder

head bolts: conventional and torque-to-yield.

Conventional bolts are tightened using a torque

wrench in steps of progressively higher torques.

Torque-to-yield bolts are also tightened in a sequence

of progressively higher torques. However, the final

step is to tighten the bolts a predetermined angle

using an angle torque gauge. This final step distorts

the threads slightly resulting in greater holding power.

Due to the fact that the cylinder head bolt threads are

distorted during the tightening sequence, torque-to-

yield bolts may only be reused when specified by the

vehicle manufacturer.

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Cylinder head bolt

1 Torque-to-yield bolt

2 Cylinder head

3 Cylinder block

4 Cylinder head gasket

42 Service Training


Valves

A valve has a round head with a tapered face that

seals against a seat in the cylinder head. Because of

its stem-and-head construction, the valve is

sometimes called a mushroom valve.

The head of the valve is the larger end that seals the

valve port. The surface of the cylinder head that seals

the port is called the valve seat. The valve head has a

machined surface called the valve face. The valve face

is the contact point between the valve and the valve

seat. Both the valve face and the valve seat must be

machined so that they form a tight seal when closed.

Full contact between the valve and valve seat is

needed to transfer heat away from the valve face into

the cylinder head. The valve margin is the thickness

of the valve head.

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Valve features

1 Collet groove

2 Head

3 Margin

4 Face

5 Stem

Service Training 43


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Valve seat features

1 Valve seat

2 Valve seat insert

Valve seat

The valve seat is the area contacted by the valve face

when the valve is in the closed position. Both intake

and exhaust valves have seats. The valve seat area

must be hard enough to withstand the constant

pounding as the valve rapidly opens and closes. The

seat must also be able to conduct heat well so that the

valve does not overheat and distort. Because exhaust

gases are corrosive, the exhaust valve seats must be

resistant to corrosion. A valve seat insert is pressed

into the cylinder head. This insert is made of a

different material from the cylinder head and has the

necessary heat, hardness, and anticorrosion

properties.

44 Service Training


Valve components

1 Cylinder head

2 Valve oil seal

3 Valve stem

4 Valve guide

5 Valve seat

Valve stem

The valve stem is the long, narrow part above the

head. The stem has a groove at the end that is used to

secure the valve into the cylinder head with keepers.

The valve spring is installed on the stem end of the

valve. The spring is compressed into position on the

valve stem with the bottom firmly pressed against the

spring seat area of the cylinder head, and the top held

in place at the top of the valve stem by a retainer and

keepers. The retainer and keepers are kept in place by

the constant pressure of the spring on them and are

locked into the groove of the valve stem, thus

providing a constant pulling on the valve into the

closed position. The valve stem fits through the valve

guide that also holds the valve in alignment in the

cylinder head.

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Service Training 45


Valve guides

The valve guides keep the valves in precise alignment

in the cylinder head. They allow the valve stem to go

through the combustion chamber to the upper cylinder

head area where the valve springs are mounted. Some

valve guides are integral with the cylinder head

casting. Other valve guides are soft alloy inserts that

are manufactured separately and pressed into the

head. The valve guide fits very closely around the

valve stem, with just enough room for lubricant and

free up-and-down movement of the stem.

Designs of three or four valves per cylinder are used

because multiple valves are more precise and

efficient. A three-valve design typically uses two

valves for intake and one valve for exhaust. A four-

valve design uses two valves each for intake and

exhaust.

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Multi-valve design valve arrangement

1 Intake valves

2 Exhaust valves

3 Cooling passages

46 Service Training


Valve clearance

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Valve clearance adjustment components

1 Adjustment shim

2 Tappet

When a valve moves to the closed position, it must be

seated firmly against the valve seat. To accomplish

this, there must not be any pressure on the stem side

of the valve. On some engines, a small space is

created between the valve stem tip and the actuating

device (rocker arm, follower, bucket, tappet). This

space is called valve clearance. Valve clearance must

be precisely adjusted to avoid excessive noise and

proper operation. If valve clearance is too large, the

engine is noisy. If valve clearance is not present, the

valve may not be able to seat firmly. Combustion

gases may leak past the valve seat and eventually burn

a hole in the valve at the leak point. Some engines are

designed to maintain valve clearance with mechanical

adjustments such as a shim.

Mechanical clearance designs may need periodic

adjustments. Some engines maintain valve clearance

automatically through hydraulic valve actuator

devices. A hydraulic device (lifter, tappet, bucket)

expands under oil hydraulic pressure to maintain

contact with the valve tip at all times. During valve

close events, oil pressure is cut off, allowing the valve

to close firmly onto the seat.

Service Training 47


Valve springs

The valve spring is responsible for closing the valve

firmly onto the valve seat. The spring is installed onto

the upper cylinder head around the valve stem. Upper

and lower spring seats prevent wear and keep the

spring in place. Collets installed into the upper spring

seat (sometime called a retainer) lock into grooves in

the valve stem and keep all components locked into

place.

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Valve spring and components

1 Collets

2 Upper spring seat

3 Spring

4 Lower spring seat

5 Valve seal

6 Valve guide

7 Valve

48 Service Training


Spring tension

The valve spring must be able to generate enough

pressure to keep the valve closed firmly against the

valve seat. The valve springs must also keep all valve

train components in contact with one another as the

engine operates at high speed. At the same time, the

valve spring cannot press so much that components

wear out prematurely. As a result, valve springs are

designed to generate just the right amount of pressure

for the engine design.

Working height

Working height is the length of the spring when it is

installed in on the cylinder head and the valve is fully

closed.

Valve working height dimensions

1 Working height measurement

2 Valve guide

3 Valve

4 Valve closed

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Service Training 49


Camshaft

The camshaft controls the valve opening and closing

events. The camshaft is driven by the crankshaft

through a gear, chain, or belt connection. The

camshaft rotates at half the speed of the crankshaft to

maintain proper timing of the four cycles of

combustion. Valve opening and closing events are

accomplished by lobes on the camshaft. Each valve in

the engine, no matter the design, has its own

corresponding camshaft lobe. Depending upon engine

design, there may be only one, or multiple camshafts

in an engine.

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Camshaft (typical)

Low-lift versus high-lift camshaft

1 Low-lift camshaft lobe

2 High-lift camshaft lobe

3 High valve lift

4 Low valve lift

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Lift

Valve lift is the distance the valve is lifted off the

valve seat when fully opened. The height of the cam

lobe and the design of the valve train determine the

amount of valve lift. A valve needs enough lift to

allow the air and fuel mixture to flow freely into the

cylinder, and for exhaust gasses to flow out of the

cylinder, without interfering with the piston or

binding the spring.

50 Service Training


Duration

Duration is the length of time the cam lobe keeps the

valve open. Duration is measured in degrees of

camshaft rotation. The shape of the cam lobe

determines the amount of duration. Changing the

duration affects the operating characteristics of the

engine regarding how much torque and power are

produced at a given engine speed.

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Short duration versus long duration

1 Long duration camshaft lobe

2 Camshaft

3 Camshaft lobes

4 Short duration camshaft lobe

Service Training 51


Overlap

Overlap is the condition where both the intake and

exhaust valves are open simultaneously.

Overlap normally occurs in the four-stoke cycle in the

last part of the exhaust stroke. In order to ensure good

airflow into the cylinder during the intake stroke, the

intake valve must begin opening before the exhaust

stroke is completed.

Overlap is controlled through camshaft lobe position.

Overlap is measured in degrees of camshaft rotation.

Changing overlap has an effect on engine

performance characteristics.

Valve overlap

1 Intake valve opens

2 Top dead center

3 Exhaust valve closes

4 Power stroke

5 Intake stroke

6 Exhaust valve opens

7 Bottom dead center

8 Intake valve closes

9 Compression stroke

10 Exhaust stroke

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52 Service Training


Overhead valve drive

In an OHV engine, where the camshaft is mounted

below the valves in the block, a crankshaft gear is

used to drive a timing chain, which drives the

camshaft gear.

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Pushrod-type (OHV) camshaft drive

1 Camshaft

2 Camshaft gear

3 Timing chain

4 Crankshaft gear

Service Training 53


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Pushrod and associated components

1 Pushrod

2 Lifter

3 Camshaft

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Pushrods

In an OHV engine, pushrods transfer the lifting

motion from the camshaft and lifters to the valves.

Pushrods are made of stiff steel tubing, with cups or

balls on the ends. On some engines, pushrods come in

varying lengths to provide an initial clearance

adjustment with hydraulic lifters.

Rocker arm and associated components

1 Shaft-pivot on rocker arm.

2 Rocker arm

3 Valve

4 Pushrod

Rocker arms

The rocker arm reverses the direction of lift from the

pushrod or camshaft to the valve.

A pivot is drilled out in the rocker arm, so the rocker

arm can run on a hollow rocker arm shaft.

54 Service Training


Valve lifters

Valve lifters transmit the lifting motion of the

cams to the valve stems. The lifter protects the

valve stem against side thrust. Lifters can be

solid or have hydraulic actuation. Lifters may

also have either a flat contact surface, or a roller

mechanism to reduce friction.

Lifter

1 Solid lifter

2 Camshaft lobe

Solid lifter

A solid lifter transmits the movement between the

cam and the valve. The solid lifter is one piece and

has no moving parts. Solid lifter equipped engines

require periodic adjustments to correct for valve train

wear and eliminate noise.

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Service Training 55


Hydraulic lifters and buckets

Hydraulic lifters not only transmit movement, they

can also offset changes in valve clearance.

The hydraulic lifter is a hydraulic cylinder which

corrects valve clearance using engine oil pressure and

internal spring pressure.

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Hydraulic lifter

1 Hydraulic lifter

2 Camshaft lobe

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Hydraulic cam bucket

1 Camshaft

2 Hydraulic lifter

3 Valve stem

56 Service Training


Roller versus flat lifters

The camshaft acting on a flat lifter creates friction. To

reduce friction, some lifters have a roller wheel built

into the lifter contact surface. The camshaft contacts

the roller wheel instead of a friction surface. The

roller finger follower is similar to a rocker arm and

has the same advantage as a roller lifter. One end of

the roller finger follower is supported by a lifter that

controls lash adjustment. The other end of the roller

finger follower actuates the valve as a camshaft rides

the roller wheel.

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Roller

1 Roller

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Solid bucket

1 Lifter

2 Camshaft

3 Lifter guide

4 Shim

Overhead camshaft (OHC) cam followers

Cam followers are another term describing

mechanical lifters. Refer to Valve lifters.

Bucket-type solid lifters

Bucket-type solid lifters, as used in OHC and DOHC

engines, offer a way of adjusting the valve clearance.

Fitting shims of different thickness can alter the

clearance between the camshaft and lifter.

58 Service Training


Overhead camshaft (OHC) hydraulic lash adjusters

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Hydraulic bucket assembly

1 Bucket body

2 Plunger

3 Check ball spring

4 Check ball

In some engines, a rocker arm-mounted hydraulic

lash adjuster fits between the valve stem and the

rocker arm. The bucket-type hydraulic lifter has a

bucket body that contains two oil chambers. A check

ball and spring control the movement of oil between

these two chambers. As the oil moves from one

chamber to the other, a spring-controlled plunger

moves up and down and contacts the top of the valve

stem.

5 Check ball cage

6 Plunger spring

7 Body

The hydraulic lash adjuster is the OHC version of the

hydraulic lifter. On many OHC engines, the valve

clearance is adjusted automatically by hydraulic lash

adjusters. Hydraulic lash adjusters eliminate the need

for manual valve adjustments. A bucket-type

hydraulic lash adjuster is positioned between the top

of the valve stem and the camshaft. In this design, the

camshaft directly contacts the top of the lash adjuster.

Service Training 59


Rocker arm-mounted hydraulic lash adjuster

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Rocker arm-mounted hydraulic lash adjusters

1 Rocker arms

2 Hydraulic lifters

3 Camshafts

A rocker arm-mounted hydraulic lash adjuster

operates much like bucket-type hydraulic lash

adjuster, except that it is in contact with a rocker arm

rather than the camshaft.

A hydraulic lash adjuster mounted on a rocker arm

does not have a bucket body, but the check ball,

plunger, and body work the same way as a bucket-

type hydraulic lash adjuster to maintain zero valve

clearance.

60 Service Training


Overhead cam drive

To drive the camshaft(s), a pulley on the end of the

crankshaft drives a timing belt or timing chain that

turns the camshaft pulley(s). The camshaft pulleys

connected to the chain or belt then turn each

camshaft. The timing belt pulley has half as many

teeth as the camshaft pulleys, so the camshafts turn

once for every two turns of the crankshaft. OHC

drives also include a tensioner pulley and tensioner

spring or hydraulic auto tensioner, which maintain

timing chain or belt tension and valve timing.

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Overhead camshaft drive (belt)

1 Tensioner

2 Idler pulley

Service Training 61


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Belt and chain camshaft drive

1 Camshaft pulley

2 Camshaft chain

3 Chain tensioner

4 Intake camshaft

5 Exhaust camshaft

6 Timing belt pulley

7 Timing belt

8 Tensioner pulley

Belt and chain drive

Another type of DOHC drive is the combination belt

and chain drive. In this design, a timing belt drives the

intake camshaft, and a timing chain drives the exhaust

camshaft. The major advantage of this design is that it

allows the valves to be placed at a more vertical

angle. This angle produces enhanced combustion

efficiency, better fuel economy, and lower emissions.

62 Service Training


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1 Driven camshaft

2 Drive camshaft

3 Helical gears

4 Timing belt

5 Friction gear

Belt and gear drive

This dual overhead camshaft (DOHC) arrangement

uses a belt and pulley attached to one camshaft and

the crankshaft. The second camshaft is connected to

the first using helical-cut gears. One of the helical

gears has one more tooth than the other. The gear with

the extra tooth is called a friction gear because it

causes a slight binding condition between the gears.

This binding action helps reduce noise in the gears

and valve train during operation.

Service Training 63

Lesson 3 – Valve train Theory

Variable camshaft timing gear assembly

1 Body and sprocket assembly

2 Inner sleeve

3 Return spring

4 Piston

5 Ring gears

6 Oil pressure

Variable cam timing

Some DOHC engines utilize variable cam timing

(VCT). A similar system is known as variable valve

timing (VVT). In either system, a hydraulic actuator

changes the valve timing of the camshafts. The

camshaft timing is changed dependent upon engine

load and speed to improve engine performance.

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64 Service Training

General Lesson 4 – Lubrication system

Objectives


� Explain the purpose and function of the lubrication system.

� Describe the lubrication system of a modern internal combustion engine.

� Identify the main components of the lubrication system.

� Describe the theory and operation of the lubrication system.

Service Training 65

Lesson 4 – Lubrication system At a glance

Description

Engine lubrication system

A large amount of heat is created during engine

operation. The heat created between some moving

parts is so great that an internal combustion engine

cannot operate for long before damage will occur. The

lubrication system provides a steady supply of

pressurized oil to the moving parts of the engine.

Lubrication reduces friction heat and keeps parts from

wearing against each other. Oil also helps cool the

engine, wash away dirt and debris, and reduce noise.

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The major components of the lubrication system

include:

� Oil pan

� Oil strainer

� Oil pump

� Oil filter

� Oil seals

� Dipstick

� Oil pressure indicator

� Sealing materials

66 Service Training

Theory Lesson 4 – Lubrication system

Motor oil

Today’s motor oils are made from either naturally

occurring crude oil (petroleum) or from man-made

chemical compounds (synthetics). Some motor oils

are made from both and are called partial synthetics.

Motor oils are categorized according to SAE viscosity

classes as defined by the Society of Automotive

Engineers (SAE). Viscosity is an expression of the

ability of a fluid to flow or move. A thick oil at a

given temperature does not flow as quickly as a

thinner oil at the same temperature, therefore the

thicker oil will have a higher viscosity number. Oils

are graded according to their viscosity in relation to

ambient temperature. Viscosity is an indication of the

characteristics of an oil at a given temperature. The

viscosity information says nothing about the quality

of the oil.

Motor oil viscosity grade

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Lesson 4 – Lubrication system Theory

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Single viscosity oil at low and high temperature

1 Oil flow at low temperature

2 Oil flow at high temperature

There are single grade oils and multigrade oils in use

today in internal combustion engines. A single grade

oil is an oil which performs to its grade through the

entire range of temperature. A multigrade oil is an oil

which performs differently cold than when it is hot. A

multigrade oil can be made to act like a thin oil when

cold temperatures tend to thicken liquids and act like

a thick oil when hot temperatures tend to thin liquids.

Multigrade oils are also called multi-viscosity oils.

68 Service Training

Theory Lesson 4 – Lubrication system

Motor oil (continued)

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High viscosity oil and low viscosity oil at low temperature

1 High viscosity oil at low temperature

2 Low viscosity oil at low temperature

Service Training 69

Lesson 4 – Lubrication system Theory

Viscosity temperature application

1 Synthetic motor oil

2 High-performance high lubricity motor oil

3 Super multigrade motor oil

4 Super multigrade motor oil

5 Ambient temperature

SAE numbers tell the temperature range that the oil

will lubricate best. An SAE 10 classified oil lubricates

well at low temperatures but becomes thin at high

temperatures. An SAE 30 classified oil lubricates well

at mid-range temperatures but becomes thick at low

temperatures. Multigrade oils cover more than one

SAE viscosity number. Their designations include the

two viscosity numbers that the oil has met. For

example, SAE 10W30 oil meets the requirements of a

10 weight oil for cold start and cold lubrication, and

the requirements of a 30 weight oil for mid

temperature lubrication.

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70 Service Training

Operation Lesson 4 – Lubrication system

Oil circulation

Oil circulates through the engine as follows:

� The oil in the oil pan is drawn up through the oil

strainer by the oil pump. The strainer filters out

large particles.

� Oil flows through the oil filter, which filters

smaller particles of dirt and debris.

� From the oil filter, the oil flows into the main oil

passage (or gallery) in the cylinder block.

� From the main gallery, oil flows through smaller

passages to the camshaft, pistons, crankshaft, and

other moving parts. Oil holes and jets direct the

flow of oil to critical parts, such as bearings and

pistons.

� As the oil lubricates the surfaces of moving parts,

it is constantly pushed off by new oil. The oil drips

from the lubricated surfaces back into the oil pan.

In many engines, an oil cooler is used to cool the

oil before the oil is drawn back through the oil

strainer to repeat the cycle. Oil circulation

1 Upper oil gallery oil flow

2 Filter oil flow

3 Main gallery oil flow

4 Oil pan oil source

5 Oil strainer to oil pump oil flow

6 Oil pump

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Service Training 71

Lesson 4 – Lubrication system Operation

Pressure lubrication

Oil circulation

1 Oil filter

2 Oil pressure switch or sending unit

3 Hydraulic bucket lifter

4 Oil splash nozzles

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Oil drips off the moving parts into the oil pan. A

pump draws the oil from the pan, through a strainer,

and forces it under pressure through a filter. After

filtering, the oil passes to the lubricating points in the

cylinder head and the cylinder block. A pressure relief

valve in the oil pump ensures that oil pressure does

not exceed engine oil pressure specifications.

5 Oil pan

6 Oil intake pipe and strainer

7 Oil pump

Full pressure is used to pump oil through the main oil

gallery. Oil from the main gallery lubricates the

crankshaft main bearings, connecting rod bearings,

camshaft, and hydraulic valve lifters (if equipped). In

other parts of the engine, the volume is reduced as oil

flows through smaller passages. Pushrod ends and

rocker arms receive reduced pressure lubrication.

72 Service Training

Operation Lesson 4 – Lubrication system

Stresses on the oil

The lubricating oil in the engine is subjected to great

stresses from temperature and contamination. The oil

must retain its lubricating ability at temperatures of

up to 150° C (300º F). Oil coolers are sometimes used

to keep engine oil from getting too hot. Oil coolers

transfer heat from oil to the outside air or to engine

coolant. The oil is also subjected to chemical stresses

from combustion gases, dust, metal particles from

wear, and combustion residues. The high temperature

and contaminants reduce the ability of the oil to

perform well and lead to the formation of sludge.

Oil changes

It is important to change the engine oil at the

specified service intervals. The oil filter should

always be changed when changing engine oil. When

adding new oil, it is important to use the correct type,

quantity, and quality specified by the manufacturer.

Overfilling or underfilling of the engine oil can lead

to internal engine damage and high exhaust

emissions.

Service Training 73

Lesson 4 – Lubrication system Components

Oil pan components

The oil pan is attached to the bottom of the engine

block. The oil pan provides a reservoir for engine oil

and seals the crankcase. The oil pan helps dissipate

some heat from the oil into the surrounding air. Some

oil pans have a baffle that helps reduce oil sloshing in

the pan during engine operation.

Oil strainer

The oil strainer is a screen that blocks dirt and debris

from entering the oil pump inlet. The oil strainer is

located in the bottom of the oil pan attached to the

inlet side of the oil pump. The strainer is kept

completely covered by the engine oil so that air is not

sucked into the oil pump. Oil enters through the

strainer into the oil pump inlet, then is pushed

throughout the engine.

Oil pan and strainer

1 Pick-up tube

2 Strainer

3 Oil pan

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74 Service Training

Components Lesson 4 – Lubrication system

Oil pump

The oil pump provides the “push” that circulates

pressurized oil throughout the engine. The oil pump

pulls oil from the oil pan and pushes the oil through

the lubrication system. The oil pump is usually

mounted on the cylinder block or the front engine

cover. The oil pump is normally driven by the

crankshaft or camshaft using a gear, belt, or drive

shaft. Engine oil pumps are classified as positive

displacement pumps. All oil entering the pump inlet

comes out the pump outlet. Oil is not allowed to

circulate inside the pump.

Pressure relief valve

Excessive oil pressure damages seals and gaskets,

causing oil leaks. The faster an oil pump is driven, the

more oil it pumps. Lubrication systems include a

pressure relief valve that limits the maximum

pressure that the pump can develop. If all the oil from

the pump is forced into the oil passages, the oil would

quickly heat up and break down. To limit the oil

pressure, the pressure relief valve opens at a preset

limit and sends some of the oil from the pump outlet

back into the inlet or back into the oil pan.

Service Training 75


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Rotor-type oil pump

1 Inner rotor

2 Outer rotor

3 Outlet port

4 Pressure relief valve

5 Inlet port

6 Engine oil

7 Pump body

Oil pump types

Rotor-type pump

A rotor-type pump uses two rotors, one turning inside

the other, to pressurize the oil. The two rotors turn at

slightly different speeds. The rotors have smooth,

rounded lobes. These types of rotors are called

trochoid gears.

In this design, the crankshaft drives the inner rotor.

The inner rotor drives the outer rotor. As the two

rotors turn, pumping cavities are formed between the

lobes on the two rotors. The pumping cavities become

smaller and larger as the lobes on the two rotors go

into and out of mesh. An opening in the pump

housing at the meshing (pump outlet) and de-mesh

(pump inlet) points allows oil into and out of the

pump as the rotors spin.

Rotor-type pumps are very reliable and can withstand

high speed operation. Rotor-type pumps produce a

smooth flow of oil, rather than a pulsing action. The

rotor-type pump used on many engines has a small

hole at the outlet side to allow air to escape. If there is

no oil in the pump because the vehicle has not been

driven for a long time, the air hole vents the air

quickly when the engine is started, allowing oil to

flow almost immediately to critical engine parts.

76 Service Training


Oil pump types (continued)

Gear pump

In a gear-type oil pump, two gears are used to push

the oil through the pump. The camshaft or crankshaft

drives the drive gear. As the drive gear turns, it

meshes with the driven gear, which turns in the

opposite direction. As the gears turn within the pump

body, they create a suction at the inlet port. The oil is

pulled between the gears and the pump body to the

outlet port.

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Gear-type oil pump

1 Drive gear

2 Outlet port

3 Driven gear

4 Inlet port

Service Training 77


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Oil filter and flow

1 Bypass valve (closed)

2 Anti-drainback diaphragm

3 Bypass valve spring

Oil filter

The oil filter traps smaller particles of metal, dirt, and

debris carried by the oil so they do not recirculate

through the engine. The filter keeps the oil clean to

reduce engine wear. The oil filter traps very small

particles that may get through the oil strainer. Most

oil filters are the full-flow type. All the oil pumped by

the oil pump passes through the oil filter. The filter

contains a paper element that screens out particles in

the oil. Oil flows from the oil pump and enters the oil

filter through several holes. The oil first flows around

the outer part of the filter element. Then the oil passes

through the filter material into the center of the

element. Finally, the oil flows out to the main gallery

through a tube in the center of the filter.

The filter screws onto the main oil gallery tube. A seal

prevents oil from leaking at the connection between

the filter and the cylinder block.

78 Service Training


Oil filter (continued)

Bypass valve

As the element in the oil filter becomes dirty, the oil

pump works harder to push oil through the filter. If

the filter becomes clogged, and no way is provided to

bypass the filter, engine damage could result. To

prevent this type of damage, most original equipment

manufacturer (OEM) oil filters also include a spring-

loaded bypass valve. This valve is designed to allow

oil to bypass the filter if the filter becomes clogged.

When back-pressure becomes great enough to

overcome the spring on the bypass valve, the valve

opens, allowing some of the oil to bypass the filter

and go directly to the oil gallery tube.

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Oil filter normal filtered flow

1 Filter element

2 Filtered oil out

3 Unfiltered oil in

4 Bypass valve spring

5 Bypass valve (closed)

Service Training 79


Oil filter bypass flow (unfiltered)

1 Filter element

2 Anti-drainback valve

3 Unfiltered bypass oil out

4 Unfiltered oil in

5 Oil flow past open bypass valve

Anti-drainback diaphragm

Many OEM oil filters also contain an anti-drainback

diaphragm, which keeps oil inside the filter when the

engine is shut off. The diaphragm covers all the filter

inlet holes when the oil pump stops. When the engine

is shut off, the pressure of the oil in the filter forces

the diaphragm down on the holes, sealing oil in the

filter. When the engine starts again, oil flows

immediately from the filter allowing critical engine

parts to receive lubrication immediately. As the

pressure from the oil pump grows, the diaphragm is

pushed away from the holes and normal oil flow

begins again.

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80 Service Training


Oil seals

At various locations in the engine, seals and gaskets

keep oil from leaking out of the engine or into places

in the engine where oil should not be present.

Dipstick

The engine oil dipstick is used to measure the level of

oil in the oil pan. One end of the dipstick dips into the

top of the oil reservoir, and the other end has a handle

so it can be pulled out easily. The end that dips into

the oil pan has a gauge on it that shows whether oil

should be added to the engine.

It is important to keep the oil level above the

“MIN” line at all times. The crankcase should never

be overfilled or allowed to drop too low. Too much oil

may permit the crankshaft to contact the oil and churn

it until it turns to foam. The oil pump cannot pump

foam, and foam will not lubricate. Low oil levels can

result in excessively high oil temperatures, which may

lead to bearing failure. An oil level that is too high or

too low can also increase oil consumption. Consult

the Workshop Manual or Owner’s Manual for the

correct oil capacity and recommended oil.

Oil pressure warning indicator

The instrument panel usually has some type of oil

pressure indicator that warns the driver when the

lubrication system cannot maintain the oil pressure

needed by the engine. This indicator may be a gauge

or a warning light.

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Oil dipstick and markings

1 Maximum oil level

2 Minimum oil level

3 Bottom tip of dipstick

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Instrument cluster oil pressure warning indicator

Service Training 81

Lesson 5 – Intake air system General

Objectives


� Explain the purpose and function of the intake air system.

� Identify components of the intake air system.

� Describe the intake air system of the internal combustion engine.

� Explain the theory and operation of the intake air system.

82 Service Training

At a glance Lesson 5 – Intake air system

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Air intake system

Air intake manifold

1 Intake manifold

The air intake system is designed to clean the intake

air and feed the air and fuel mixture to the cylinders.

The major components of the air intake system

includes:

� Air intake ducting

� Air induction resonator

� Air cleaner assembly

� Intake manifold

Resonator assemblies may be included to reduce air

intake noise. Air induction resonators can be separate

components or part of the air intake housing (i.e.,

conical air cleaner). Additionally, a mass air flow

sensor and a throttle body which are both part of the

fuel injection system are located between the air

cleaner assembly and the intake manifold. Refer to

Engine Performance for information about the fuel

injection system.

Service Training 83

Lesson 5 – Intake air system Components

Air cleaner and intake components

The air cleaner assembly houses the air filter element.

The filter element removes any particles of dirt, dust,

or debris entering the air intake system. The intake

manifold directs intake air into the cylinders. Intake

manifolds are made of aluminum alloy or plastic

composites. To ensure good cylinder charging, intake

manifolds must have a very smooth internal surface

offering minimal resistance to the inflowing gases.

The shape of the intake manifold can cause the air

flow to swirl all the way into the combustion chamber

for more efficient combustion. If the ports to the

individual cylinders are the same length and diameter,

the same conditions apply at all the cylinders during

induction, resulting in uniform cylinder charging.

During the warm-up phase, some of the fuel

condenses on the internal walls of the intake

manifold. To minimize these condensation losses,

intake manifolds are often fitted with a pre-heater.

Intake systems must be perfectly sealed from the

outside. Unmetered air induced through leaks disturbs

engine management and results in uneven engine

operation, especially at idle. Refer to the Engine

Performance Fundamentals book for information

regarding the engine management system. The

vacuum in the intake manifold can be used for various

purposes. Brake servos and automatic choke systems

can be operated by means of vacuum diaphragm

units. Appropriate connectors are provided on the

intake manifold for these different functions.

84 Service Training

Components Lesson 5 – Intake air system

Inlet runners

The length and diameter of the intake manifold inlet

runners also have an effect on volumetric efficiency.

During low engine speeds, longer and thinner inlet

runners produce higher volumetric efficiency. During

high engine speeds, shorter and wider inlet runners

are more efficient. More modern engine designs

utilize such innovations as multi-valve engines and

variable intake systems to increase volumetric

efficiency.

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Inlet runners

1 Shorter, thicker inlet runners

2 Longer, thinner inlet runners

Variable induction systems

Because the length and diameter of the intake runners

affect performance, efficiency and exhaust emissions,

some engines utilize variable length induction

systems. These systems use both long and short intake

runners. At lower engine speeds, the air flows through

the long runners for best performance. At a certain

engine speed, a valve opens to allow air also to flow

through the short runners for maximum output at high

engine speeds. These intake subsystems are used to

provide increased air flow when required to improve

torque and performance. There are basic two types of

variable length intake manifold designs:

� Intake manifold runner control (IMRC) actuated

system and

� Intake manifold tuning (IMT) valve

Service Training 85


Intake manifold runner control (IMRC) system

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IMRC components

1 Upper intake manifold

2 Upper manifold gaskets

3 IMRC assemblies (lower intake manifold)

4 IMRC actuator

5 Air inlet

The intake manifold has two runners per cylinder,

feeding each of the intake ports in the cylinder heads.

The IMRC assemblies are located between the intake

manifold and cylinder heads, providing two air

passages for each cylinder. The IMRC assemblies are

actually the lower manifold, in what becomes a two

piece intake manifold assembly. One air passage is

always open and the other passage switches from

closed to open by means of a valve plate.

Below a certain rpm, generally 3,000 rpm, the valve

plate is closed to improve low speed and cold engine

performance. Above this rpm, the valve plate opens to

improve high speed engine performance. The valve

plates are opened and closed by the IMRC actuator.

Most actuator designs are electric in operation. Some

actuators are vacuum operated. The engine control

system controls the IMRC actuator. Refer to the

Engine Performance book for information about the

engine control system.

86 Service Training

Components Lesson 5 – Intake air system

Intake manifold tuning (IMT) valve

The IMT valve is an electric actuator controlling a

valve plate or shutter device mounted directly to the

intake manifold. Below a certain rpm the IMT valve

is closed. Above a certain rpm, the IMT valve opens

allowing more into the cylinders to improve high

speed engine performance. The engine control system

controls the IMT valve. Refer to the Engine

Performance book for information about the engine

control system.

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IMTV components

1 Intake airflow

2 Manifold gasket

3 Manifold to cylinder head gaskets

4 Cylinder heads

5 IMT valve

6 Lower intake manifold

7 Upper intake manifold

Service Training 87


Forced induction

Most vehicle engines draw in the air-fuel mixture

from vacuum created by the downward travel of the

piston, and for this reason are called naturally

aspirated engines. Naturally aspirated engines rely on

atmospheric air pressure to supply air to the cylinder.

The power output of an engine is directly linked to its

volumetric efficiency. A naturally aspirated engine

usually has about an 80% volumetric efficiency. This

means that the engine draws in about 80% of its

displacement. Streamlining passages and increasing

port sizes improves volumetric efficiency. The air still

has difficulty reaching the cylinder. As long as the

engine relies on atmospheric pressure to push the air

through the intake system, the engine does not

produce as much power as it is capable of producing.

Without external help, an engine receives only a

partial air-fuel charge. Pumping air into the cylinders

can increase the air-fuel charge. This forcing of more

air into the cylinders allows the engine to fill its

cylinders with a charge, which meets or exceeds

100% volumetric efficiency. This process of pumping

more air into the engine cylinders is called forced

induction. There are two different methods used to

pump air into an engine: turbocharging and

supercharging.

88 Service Training

Theory Lesson 5 – Intake air system

Turbocharging

Turbocharger system

1 Compressor shaft oil feed

2 Turbine

3 Turbine exhaust out

4 Compressor shaft oil drain

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A large turbocharger unit generates more torque, but

responds more slowly at low engine speeds. A smaller

turbocharger unit has a smaller turbine wheel, which

is easier to set in motion. Some vehicle manufacturers

have begun using smaller turbocharger units, which

begin charging at low engine speeds and provide full

effect during “normal driving”. These smaller

turbocharger units are often called light pressure

turbochargers.

5 Compressor

6 Compressor air intake

7 Air intercooler

The most common type of air pump or compressor is

a turbocharger. The turbocharger uses exhaust gas to

drive a turbine wheel attached to a shaft and

connected to a compressor wheel. The exhaust gas

flow sets the turbine wheel in motion, which in turn

powers the compressor wheel located in the intake

pipe. The compressor wheel compresses the air and

forces it into the engine at pressures up to about 9 psi.

To ensure that the pressure in the turbocharger unit

does not become too high and damage the engine, a

pressure-regulating valve called a wastegate is used.

The wastegate opens at a certain pre-set pressure.

Service Training 89

Lesson 5 – Intake air systems Theory

Because a turbocharger is driven by exhaust gas flow,

it does not consume engine power. Some

turbocharged engines experience a short interval of

time before the turbocharger begins to pump a large

amount of air into the engine. This short interval of

time is called turbo lag. During this period of turbo

lag, the engine does not deliver the extra power that

the turbocharger provides at higher rpm. Some

turbochargers use a variable inlet design. This design

helps the turbocharger reach optimal speed at a lower

rpm which increases low-speed engine performance

and reduces turbo lag.

Compressor and turbine housing

1 Fresh air intake

2 Oil feed

3 Exhaust out

4 Exhaust in

5 Compressed air to engine

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90 Service Training

Theory Lesson 5 – Intake air system

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Supercharging

Lobe-type supercharger

1 Lobe-type compressor rotors

2 Supercharger assembly

A supercharger is a type of air pump or compressor.

Exhaust gases do not drive a supercharger. The power

source of a supercharger is the engine itself. The

crankshaft drives the supercharger through a belt, gear

or chain. Intake manifold pressures of up to 13 psi are

typical for supercharged engines.

As with a turbocharger, the amount of power available

to drive the supercharger depends upon engine speed.

Unlike some turbocharged engines, when accelerating

a supercharger immediately delivers extra engine

power. Although it takes engine power to drive a

supercharger, a supercharger helps produce much

more power in return. There are different types of

superchargers. No matter how a supercharger is

designed, its main purpose is to force more air into

the cylinders and help the engine produce more

power.

Service Training 91

Lesson 6 – Exhaust system General

Objectives


� Explain the purpose and function of the exhaust system.

� Describe the exhaust system and identify types.

� Identify the components of the exhaust system.

� Explain the theory and operation of the exhaust system.

92 Service Training

At a glance Lesson 6 – Exhaust system

Description and purpose

The exhaust system carries the engine exhaust gases

to the rear of the vehicle, dampens the noise produced

by combustion and cleans the exhaust gases (when

applicable).

The major components of the exhaust system include:

� Exhaust manifold

� Exhaust pipes

� Mufflers

� Catalytic converter

Exhaust systems are specifically tuned to particular

engines and vehicles. This tuning allows the optimum

combination of engine performance and noise

reduction. Because the exhaust manifold is the part of

the exhaust system exposed to the highest

temperatures, it is made of a durable metal such as

cast iron or steel. The exhaust pipes and mufflers can

be made of sheet metal or stainless steel. The exhaust

system is subjected to corrosion from water and road

salt. High temperatures and vibration also reduce

exhaust system life.

If the exhaust system is damaged or leaking, it must

be repaired or renewed. Otherwise, toxic exhaust

gases can get into the passenger compartment of the

vehicle. In addition, the engine management system is

affected adversely by air getting into the exhaust

system. Refer to the Engine Performance

Fundamentals book for information about the engine

management system.

Service Training 93

Lesson 6 – Exhaust system At a glance

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Exhaust system (typical)

1 Exhaust manifold

2 Catalytic converter

3 Muffler

4 Exhaust pipe

5 Flexible pipe

Flexible lengths of pipe give the exhaust system

limited scope for movement. Flexible pipe ensures

that thermal expansion and vibration cannot cause

stresses in the material. Flexible pipe helps reduce

noise and failures from stress.

94 Service Training

Components Lesson 6 – Exhaust system

Mufflers

The muffler reduces the level of noise produced by

the engine, and it also reduces the noise produced by

exhaust gases as they travel from the catalytic

converter to the atmosphere.

Mufflers are usually treated during manufacturing

with an anti-corrosive coating agent to increase the

life of the muffler.

Catalytic converter

The concentration of exhaust gas products released to

the atmosphere must be controlled. The catalytic

converter assists in this task. A catalyst is a material

that remains unchanged when it initiates and

increases the speed of a chemical reaction. A catalyst

will also enable a chemical reaction to occur at a

lower temperature.

The catalytic converter contains a catalyst in the form

of a specially treated honeycomb structure. As the

exhaust gases come in contact with the catalyst, they

are chemically changed into less harmful gases. Refer

to Engine Performance (TF1010008S) for further

details.

Service Training 95

Lesson 7 – Cooling system General

Objectives


� Describe the cooling system and identify types.

� Identify the components of a typical automotive cooling system.

� Explain the theory and operation of the cooling system.

96 Service Training

At a glance Lesson 7 – Cooling system

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Description

Cooling system

1 Coolant pump

2 Coolant passages

3 Thermostat

4 Radiator reservoir and degas bottle

Most engines are cooled by a steady flow of liquid

coolant through the cylinder block and heads. The

cooling system removes excess heat produced during

combustion and keeps the engine operating at its most

efficient temperature. If the cooling system fails, the

engine can overheat and may be damaged. An

operating temperature that is too cool results in

incomplete combustion and poor gas mileage.

5 Fan

6 Pressure cap

7 Radiator

The cooling system maintains an efficient engine

operating temperature. About one third of the heat

created by combustion is removed by the cooling

system. The method used to cool automotive engines

in the vast majority of applications is liquid cooling.

Service Training 97

Lesson 7 – Cooling system At a glance

Coolant

Cooling system flow

1 Flow into cylinder head

2 Flow to throttle body

3 Flow to thermostat and bypass

4 Flow into radiator

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Some vehicles use Organic Acid Technology (OAT)

coolant. OAT coolant is designed to be an extended

life coolant, reducing cooling system maintenance.

OAT coolant is orange in color to distinguish it from

other coolants and has special additives to lubricate

and protect the cooling system from corrosion. OAT

coolant is not compatible with other coolants.

5 Flow out of radiator

6 Flow into cylinder block

7 Flow from cylinder block into cylinder head

Coolant passages are cast into the cylinder block and

cylinder head. These passages carry coolant around

the cylinders and combustion chambers. The coolant

picks up heat and carries it away from these parts.

In early engines, water alone was used as coolant.

Today, most engines use an ethylene-glycol based

coolant mixed with water. Ethylene-glycol coolant

lowers the freezing point of water, raises the boiling

point of water, adds water pump lubrication, and

prevents engine corrosion.

98 Service Training

At a glance Lesson 7 – Cooling system

Operation

When a cold engine is started, the coolant pump only

circulates coolant through the cylinder head and

engine block coolant passages, quickly raising the

engine temperature. Some of the coolant may be

diverted to the heating system, which heats the

passenger compartment of the vehicle.

When enough heat is created to open the thermostat,

the water pump circulates coolant throughout the

engine and into the radiator. The hot coolant flows

from the upper tank of the radiator to the lower

radiator tank. Cool air passing over the radiator fins

removes heat from the coolant. From the lower tank,

coolant flows through the lower radiator hose to the

coolant pump inlet. The coolant pump circulates the

coolant through the pump outlet into the cylinder

block coolant passage. Coolant flows from the

cylinder block passage into the cylinder head coolant

passage to complete the circuit.

Service Training 99

Lesson 7 – Cooling system Components

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Impeller-type pump

1 Impeller

2 Pump outlet

3 Pump inlet

Coolant pump

The coolant pump circulates coolant throughout the

cooling system. Most coolant pumps are impeller or

non-positive displacement pumps. All the coolant that

enters the pump does not necessarily have to come

out of the pump. This design is different from the oil

pump (a positive displacement type), in which all the

oil that enters the pump is pumped out.

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Coolant pump (typical)

1 Coolant pump

2 Crankshaft pulley

3 Coolant pump drive pulley

Impeller-type pump

Coolant pumps are usually designed as simple

impeller-type pumps. The coolant pump has a pump

body, which holds the impeller. The impeller turns on

a shaft that is connected to a drive pulley.

The impeller-type pump operates on centrifugal

action. Centrifugal action is the tendency of a rotating

weight to be pushed outward. Coolant flows through

the pump inlet and enters the center of the impeller.

As the impeller rotates, it “slings” the coolant to the

outside edges of the impeller. The coolant is trapped

by the pump body and forced into the pump outlet.

100 Service Training

Components Lesson 7 – Cooling system

Thermostat

The thermostat restricts the flow of coolant through

the system until the engine reaches its operating

temperature. The engine warms up quickly, improving

fuel economy and emissions. A quick warm-up also

reduces combustion chamber gases blowing by the

pistons and entering the crankcase.

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Wax pellet-type thermostat

1 Valve

2 Wax

3 Spring

4 Coolant flow

Service Training 101


The thermostat contains a heat-sensitive wax pellet.

When the engine is cold, the wax remains solid, and

the spring holds the valve closed. When the coolant

heats up, the wax turns to liquid and expands. The

expansion pushes the body of the valve down, which

opens the flow of coolant to the radiator.

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Thermostat coolant flow

1 Coolant flow

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Jiggle pin

1 Jiggle pin open

2 Jiggle pin closed

3 Thermostat housing

4 Jiggle pin

To provide an outlet for air in the cooling system,

many thermostats include a jiggle pin, near the top of

the engine either in the thermostat itself or in the

thermostat housing. When there is air in the cooling

system, the weighted end of the jiggle pin drops

down, allowing air to escape. When the engine is

operating, pressure from the water pump pushes the

jiggle pin against its seat. The closed jiggle pin

prevents coolant from flowing to the radiator until the

thermostat opens.



Cooling fan

The radiator fan pulls cool outside air over the

radiator surface to pick up heat from the coolant for

faster heat transfer, especially during idling. Most

vehicles equipped with air conditioning usually have

an additional fan for increased cooling. Most fans

have four or more blades to increase their cooling

capacity. A fan shroud may surround the fan to

concentrate the flow of air.

Cooling fan drives

There are several different types of fan drive

including electric, viscous, hydraulic and mechanical.

Some vehicles may use a combination of two

different types of fan drives. Some fans are driven by

an electric motor which turns the fan on and off

depending upon engine coolant temperature. When

the coolant reaches a preset temperature, the

thermoswitch (engine coolant temperature sensor)

activates an electrical relay, which turns on the fan

motor. When the coolant temperature drops, the

thermoswitch turns off the fan motor. Other fans are

controlled by a microprocessor-based control module.

Sensors send engine coolant temperature data to the

module which uses the data to determine if the engine

coolant fan should be switched on or off.

A hydraulic fan drive uses hydraulic oil pressure to

drive the fan.



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Viscous fan clutch and bi-metal spring

1 Clutch plate

2 Bi-metal thermostat

A mechanical fan drive uses a pulley and belt to drive

the fan. Most mechanical drive fans use a clutch

drive, which allows the fan to turn at lower speeds

when the temperature is lower. If the fan were

constantly turned at the speed of the engine, the fan

would become very noisy at high speeds and would

also sap engine power.

One of the most common types of fan clutches is the

viscous type. A viscous drive is a fluid coupling.

A bi-metal thermostat controls the amount of

coupling. The bi-metal thermostat is a spring made of

two types of metal. The spring expands at higher

temperatures and contracts at lower temperatures. The

thermostat is connected to a valve that controls the

amount of fluid available to couple the clutch. The

thermostat responds to the temperature of the air

passing through the radiator. If the air temperature is

cold, the flow of fluid in the clutch is restricted. Little

or no coupling occurs, and the fan turns very slowly

or not at all. At higher temperatures, the fluid

operating on the clutch increases, causing a tighter

coupling and faster fan speed.



Coolant overflow reservoir and degas bottle

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Coolant reservoir

1 Overflow tube

2 Coolant flow to or from radiator

3 Radiator reservoir hose

Two types of coolant overflow reservoirs are

commonly used: a non-pressurized coolant overflow

reservoir, and a pressurized type of reservoir known

as a degas bottle.

As coolant becomes hot, it expands. The non-

pressurized coolant recovery reservoir stores the

excess coolant released from the radiator. When the

engine cools, the coolant in the reservoir is drawn

back into the cooling system. This keeps the cooling

system constantly full, increasing cooling system

efficiency.

Coolant level is checked and coolant is added at the

radiator. A hose connects the reservoir to the radiator

filler neck. As engine temperature rises, a pressure

cap permits the expanding coolant to flow from the

radiator into the reservoir as required. When the

engine is stopped, the coolant temperature drops and

the coolant contracts. A partial vacuum develops in

the cooling system, drawing coolant from the

reservoir back into the cooling system. The reservoir

has an overflow tube that allows coolant to escape if

the cooling system is overfilled or if the engine

overheats.



Degas bottle

The degas bottle is similar in operation and

appearance to the coolant overflow reservoir.

However, the bottle is pressurized like the radiator,

and the pressure cap is located on the degas bottle

itself instead of on the radiator. The cooling system is

filled through the pressure cap located on the degas

bottle. The degas bottle provides for coolant

expansion during normal operation. An overflow tube

provides an outlet for excess coolant to escape if the

cooling system is overfilled or the engine overheats.

The degas bottle provides air separation during engine

operation. The degas bottle replenishes engine coolant

to the system.ENF099-A/VF

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Coolant degas bottle

1 Pressure cap

2 Overflow outlet

3 Coolant inlet

4 Coolant outlet



Degas bottle (continued)

Pressure cap

The pressure cap maintains pressure in the system,

which raises the boiling temperature of the coolant.

The pressure cap also allows excess pressure to

escape from the system.

The boiling point of a liquid rises with the amount of

pressure it is under. For example, water at sea level

boils at about 100º C (212º F). Water in a typical

pressurized cooling system boils at more than 121º C

(250º F). Pressurizing the cooling system effectively

raises the operating temperature of the engine. The

cooling system’s increased pressure raises the

coolant’s boiling point to add a comfortable margin

between the engine operating temperature and the

boiling point of the coolant.

The pressure cap fits on either the filler neck of the

radiator or on a degas bottle. The pressure cap

includes a pressure valve and a vacuum valve. Both

are spring-loaded to remain closed when the system is

within operating ranges.

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Radiator pressure cap (typical)

1 Pressure cap

2 Coolant flow to or from overflow reservoir

3 Overflow reservoir hose

4 Pressure valve

5 Vacuum valve

6 Spring



If the pressure in the cooling system exceeds a

specified limit, the pressure valve opens to avoid

bursting the radiator or hoses. Steam and coolant can

then escape through the reservoir hose (attached to

the filler neck) into the radiator reservoir or out the

overflow tube if the vehicle is equipped with a degas

bottle.

When the engine is shut off, steam in the system

condenses back into liquid, creating a vacuum in the

system. The vacuum valve on the pressure cap opens,

allowing coolant from the reservoir back into the

radiator through the radiator reservoir hose. Without a

vacuum valve, the radiator tanks and hoses could

collapse.

The pressure cap protects the cooling system from

springing leaks due to excess pressure or vacuum. For

the cap to work correctly, the entire cooling system

must be airtight.

Removing the radiator cap while the engine is

running, or when the engine and radiator are hot is

dangerous. Coolant and steam may escape and cause

serious injury. Turn off the engine and wait until it is

cool before removing the cap.



Crossflow

Crossflow radiator

1 Coolant outlet

2 Core

3 Right tank

4 Coolant flows from side to side

5 Outlet tube to or from coolant reservoir

6 Coolant inlet

7 Left tank

The crossflow-type radiator is commonly used. The

crossflow radiator has tanks on the side of the core, so

coolant flows through tubes from one side to the

other.

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Radiator

The radiator transfers heat from the coolant to the

outside air. The radiator core contains tubes and fins.

Coolant flows through the tubes, and the fins increase

the radiator’s surface area exposed to the air. The

increased surface area allows the air to carry away

more heat, reducing the coolant temperature.

Radiators are either crossflow or downflow in design.



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Downflow

Downflow radiator

1 Upper tank

2 Lower tank

3 Coolant outlet

4 Coolant flows downward

5 Core

6 Coolant inlet

The downflow radiator has an upper and lower tank.

Tubes connect the tanks. Coolant flows down from

the upper tank through the core and into the lower

tank. Cooling takes place as the liquid passes through

the radiator core.



In-tank transmission fluid cooler

1 Radiator tank with internal transmission fluid

cooler

2 Transmission fluid in

3 Transmission fluid out

If the vehicle has an automatic transmission, the

radiator may have a separate cooler in one of the tanks

for the automatic transmission fluid.

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Radiator (continued)


Lesson 8 – Diesel engine General

Objectives


� Explain the purpose and function of the diesel engine.

� Describe a diesel engine.

� Identify similarities and differences of diesel and gasoline engines.

� Explain the theory and operation of a diesel engine.


At a glance Lesson 8 – Diesel engine

Description

The diesel engine is a reciprocating piston engine

having the same basic structure and cycle as the

gasoline engine. The main difference between a diesel

engine and gasoline engine is the fuel used, and the

method of ignition for fuel combustion.

Operation

Diesel engines use the heat of compression to ignite

the air and fuel mixture in the combustion chamber.

This type of ignition is accomplished using a high

compression pressure and diesel fuel injected into the

combustion chamber under very high pressure. The

combination of diesel fuel and high compression

pressure produces spontaneous ignition to begin the

combustion cycle.

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Diesel engine


Lesson 8 – Diesel engine Components

Cylinder block

Diesel engine main bearing caps

1 Main bearing cap

Diesel and gasoline engine blocks look similar to

each other, but there are some construction

differences. Most diesel engines use cylinder liners

instead of having the cylinder bores cast as part of the

block. By using cylinder liners, repairs can be made

to keep the engine in service a long time. On those

diesel engines that do not use liners, the cylinder

walls are thicker than those of a similar sized gasoline

engine. Diesel engines have heavier and thicker main

webs for increased crankshaft support.

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Components Lesson 8 – Diesel engine

Wet liners

Wet-type cylinder liners in diesel engines are the

same as those used in gasoline engines. The physical

dimensions of the liner may be different in order to

tolerate the operating conditions of a diesel engine.

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Wet liner

1 Liner

2 Seal

3 Coolant

4 Cylinder block

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Crankshaft

The crankshaft used on diesel engines is of similar

construction to that of gasoline engines with two

differences:

� Diesel crankshafts are usually manufactured by

forging rather than casting. Forging makes the

crankshaft stronger.

� Diesel crankshaft journals are usually larger than

gasoline-type crankshaft journals. Larger journals

allow the crankshaft to handle greater force.Crankshaft



Connecting rods

Connecting rods used in diesel engines are usually

made of forged steel. Connecting rods used in diesel

engines differ from connecting rods used in gasoline

engines in that the end cap is offset and serrated at the

mating surface with the rod. Offset and serrated end

cap design helps keep the cap in place and reduces the

load on the connecting rod bolts.

Pistons and rings

Pistons used in light-duty diesel applications appear

similar to those used in gasoline engines. Diesel

pistons are heavier than gasoline pistons because

diesel pistons are generally made of forged steel

rather than aluminum, and the internal thickness of

the material is greater.

The compression rings used in diesel engines are

usually made of cast iron and are often coated with

chrome and molybdenum to reduce friction.

Cylinder head

Externally, the cylinder head of the diesel engine

looks much like the cylinder head on a gasoline

engine. There are many internal design differences

that make diesel engines unique.

The cylinder head itself must be much stronger and

heavier on a diesel engine in order to withstand the

greater stresses of heat and pressure. Combustion

chamber design and air passages on diesel engines

can be more complex than on a gasoline engine.

There are several designs of diesel combustion

chambers in use, but two designs are most common:

open combustion chamber and pre-combustion

chamber.



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Open combustion chamber design

Diesel fuel injection

1 Fuel injector

2 Combustion chamber

3 Inlet air passage

4 Glow plug

The most common type of diesel combustion chamber

is the open chamber, also known as the direct

injection combustion chamber. The open design relies

on the shape of the inlet air passage to cause the

intake air charge to become turbulent. Fuel is injected

directly into the combustion chamber.



Pre-combustion chamber design

The pre-combustion chamber design uses two

combustion chambers for each cylinder. A main

chamber connects by a narrow passageway to a

smaller pre-combustion chamber. The pre-combustion

chamber contains the fuel injector and is designed to

begin the combustion process. Intake air is

compressed through the narrow passageway into the

pre-combustion chamber. Fuel is sprayed into the

pre-combustion chamber where it ignites. The

burning mixture then forces its way out into the main

combustion chamber where it completes its burning

and forces the piston down.

Pre-combustion chamber

1 Fuel injector

2 Glow plug

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Valves and valve seats

Diesel engine valves are constructed of special alloys

that are able to perform well in the high heat and

pressure of the diesel engine. Some valves are

partially filled with sodium which helps them

dissipate heat. A large percentage of heat is

transferred from the valve head to the valve seat.

Particular attention must be paid to valve seat width

so that adequate heat transfer takes place.

A wide valve seat has the advantage of being able to

conduct a greater amount of heat. However, a wide

valve seat has a greater possibility of trapping carbon

deposits which may cause a valve leak. A narrow

valve seat provides better sealing than a wide valve

seat, but does not transfer the same amount of heat. A

compromise between wide and narrow seats is

necessary in the diesel engine.

Diesel engines frequently use valve seat inserts. The

inserts have the advantage of being replaceable. Valve

seat inserts are made of special metal alloys that

withstand the heat and pressure of the diesel engine.

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Sodium-filled valve

1 Bimetallic (sodium) valve

2 Single metal valve

3 Collet groove

4 Valve stem

5 Valve head

6 Valve face

7 Valve collet

8 Sodium filling

9 Armoring


Lesson 8 – Diesel engine At a glance

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Fuel delivery system

Conventional Design

In a conventional diesel fuel delivery system, fuel is

pulled from the fuel tank, filtered and delivered to a

high-pressure pump. High-pressure fuel is regulated

and delivered to a fuel rail that feeds the fuel

injectors. An injection control energizes each injector

at the appropriate moment to provide fuel in the

compression stroke for combustion.

Conventional design

1 Filter

2 High-pressure pump

3 Fuel Rails

4 Fuel injectors (8)

5 Fuel tank

Common rail diesel

Common rail design

Common rail-type diesel engines use independent

fuel pressure and fuel injection systems. A high-

pressure fuel pump draws fuel from the tank and

delivers it through a pressure regulator to a common

fuel rail. The high-pressure pump consists of a low-

pressure transfer pump and a high-pressure chamber.

Fuel injection is controlled by the Powertrain Control

Module (PCM) and an Injector Driver Module (IDM)

which regulates injector on-time based on engine

operating conditions.

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Common rail fuel injection system

1 High-pressure pump

2 Fuel temperature sensor

3 Fuel metering valve

4 Fuel pressure sensor

5 Fuel injection supply manifold

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6 Fuel injectors

7 Injector driver module (IDM)

8 Fuel tank

9 Fuel filter

In the common rail design, exhaust emission levels

are greatly reduced, and operating noise minimized,

due to greater control of the combustion process.

Fuel pressure regulation and injector timing are

controlled by the IDM and PCM, and injector design

has been modified allowing for pre and post-

combustion fuel injection events to take place at

various stages of the compression and power strokes.

The improved fuel delivery control helps produce

cleaner, more consistently timed combustion and

cylinder pressures. This has the effect of lowering

emission levels and reducing operating noise.

Fuel delivery system (continued)



Lubrication system

Diesel lubrication system

1 Oil pump

2 Oil filter

3 Adapter

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4 O-ring

5 Oil cooler

6 Oil cooler retaining bolt

The lubrication system used on diesel engines is

similar in operation to gasoline engines. Most diesels

will have some type of oil cooler to help remove heat

from the oil. The oil flows under pressure through the

galleries of the engine and returns to the crankcase.

The lubricating oil used on diesel engines is different

from that used in gasoline engines. A special oil is

needed because diesel operation produces more oil

contamination than in a gasoline engine. High carbon

content in diesel fuel causes oil in diesel engines to

become discolored soon after being put into service.

Only engine oil specifically manufactured for diesel

engines should be used.



Cooling system

Diesel engine cooling systems normally have a larger

capacity cooling system than a gasoline engine

cooling system. The temperature inside a diesel

engine must be closely controlled because it relies on

heat to burn its fuel. If the engine temperature is too

low, the following problems develop:

� Excessive wear

� Poor fuel economy

� Accumulation of water and sludge in the crankcase

� Loss of power

If the engine temperature is too high, the following

problems develop:

� Excessive wear

� Scoring

� Knock

� Burned pistons and valves

� Lubrication failure

� Seizure of moving parts

� Loss of power



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Diesel cooling system

1 Heater core

2 Thermostat

3 Fan shroud

4 Radiator

5 Coolant pump

6 Coolant expansion tank



Compression

1 Volume of cylinder at BDC

2 Compression volume at TDC

Fuel injection system

The diesel engine operates on the spontaneous

combustion, or self-ignition, principle. Intake air and

fuel are squeezed so tightly into the combustion

chamber that the molecules heat up and ignite without

the aid of an external spark. The compression ratio of

a diesel engine is much higher than the compression

ratio of a gasoline engine. Compression ratios in

naturally aspirated diesel engines are approximately

22:1. Turbo-diesel engines will have compression

ratios in the range of 16.5 – 18.5:1. Compression

pressures are produced and the air temperature rises

to approximately 500º to 800º C (932º to 1,472º F).

Diesel engines can only be operated with a fuel

injection system. Mixture formation takes place only

during the fuel injection and combustion phase.

At the end of the compression stroke, fuel is injected

into the combustion chamber where it mixes with the

hot air and ignites. The quality of this combustion

process depends on the formation of the mixture.

Since the fuel is injected so late, it does not have

much time to mix with the air. In a diesel engine the

air to fuel ratio is maintained at greater than 17:1 at

all times so that all of the fuel will burn. Refer to

Engine Performance for further details.

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Lesson 9 – Diagnostic process General

Objectives


� Explain the purpose and function of the symptom-to-system-to-component-to-cause diagnostic process.

� Explain the symptom-to-system-to-component-to-cause diagnostic process.


Overview Lesson 9 – Diagnostic process

Symptom-to-system-to-component-to-cause diagnostic process

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Symptom-to-system-to-component-to-cause

diagnostic process

1 Symptom

2 Vehicle systems

3 Components

4 Causes

Diagnosis requires a complete knowledge of the

system operation. As with all diagnosis, a technician

must use symptoms and clues to determine the cause

of a vehicle concern. To aid the technician when

diagnosing vehicles, the strategies of many successful

technicians have been analyzed and incorporated into

a diagnostic strategy and into many service

publications.

The symptom-to-system-to-component-to-causeprocess

Using the Symptom-to-System-to-Component-to-

Cause (SSCC) diagnostic process provides you with a

logical method for correcting customer concerns:

� First, confirm the “Symptom” of the customer’s

concern.

� Next, determine which “System” on the vehicle

could be causing the symptom.

� Once you identify the particular system, determine

which “Component(s)” within that system could

be the cause for the customer concern.

� After determining the faulty component(s) you

should always try to identify the cause of the

failure.

In some cases parts just wear out. However, in other

instances something other than the failed component

is responsible for the problem.


Lesson 9 – Diagnostic process Overview

For example, the customer concern is engine noise

when the vehicle is driven after sitting overnight.

After letting the engine cool, a test drive verifies the

concern. A test drive validates the “Symptom.” Next,

isolate the system(s) that are affected by the

symptom. Visual inspection does not show any

obvious causes. There are mechanical causes of

engine noise as well as electric or electronic causes.

In this case there are no other indications of

mechanical damage. Using the appropriate electronic

diagnostic equipment, diagnostic trouble code

information indicates a problem with spark timing.

Spark timing is controlled by the Powertrain Control

Module (PCM) and the electronic engine control

system. The test data validates the “System” portion

of the diagnostic process.

Next, isolate the component(s) that relate to the

system and symptom. In this case, spark timing is

adjusted by the PCM reacting to sensor input. Using

the procedures in the appropriate workshop manual,

an engine speed sensor is identified as giving faulty

input to the PCM. The sensor is the component at

fault. Following the workshop manual procedures

provides validation of the “Component” portion of the

diagnostic process.

Finally, the diagnostic process determines what the

“Cause” of the component failure is. In this case

investigation finds a broken wire in the wiring harness

to the sensor. This validates the “Cause” relating to

the component failure. Repair the wiring harness.

Workshop literature

The vehicle workshop literature contains information

for diagnostic steps and checks such as: preliminary

checks, verifying customer concern, special driving

conditions and road test and diagnostic pinpoint tests.


Engine operation List of abbreviations

BDC Bottom Dead Center position of

piston in the cylinder

Collets Keepers

DOHC Double OverHead Camshaft engine

design

Coolant

Pump Water pump

IDM Injection Driver Module

Keepers Collets

Inlet Intake

IMRC Intake Manifold Runner Control

IMTV Intake Manifold Tuning Valve

OAT Organic Acid Technology coolant

OEM Original Equipment Manufacturer

OHC Overhead Camshaft engine design

OHV OverHead Valve engine design. Also

known as pushrod-type engine.

Petrol Gasoline

PCM Powertrain Control Module

PSI Pounds per Square Inch

Pushrod-type

engine Overhead Valve (OHV) design

SAE Society of Automotive Engineers

SOHC Single OverHead Camshaft engine

design

TDC Top Dead Center position of piston in

the cylinder

VCT Variable Camshaft Timing. Also

known as Variable Valve Timing

(VVT).

VVT Variable Valve Timing. Also known

as Variable Camshaft Timing (VCT).

Water Pump Coolant pump

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